Sonar devices are frequently used by sport fisherman and boaters. These devices include means for generating high-frequency sound pulses and receiver/transducer means responsive to reflected sound pulses for acquiring target data such as the location of fish and underwater obstacles, and the depth of the bottom of the body of water. Typically, the sonar apparatus generates a series of pulses of sound at periodic intervals, receives reflected sound pulses or echoes from underwater objects, and displays either a depth readout of a target or the location of a target on a linear or curvilinear array scaled as to depth, which is a function of the time elapsed between the transmission of the sound pulses until reception of the reflected echo.
All fish finders consist of two main components, the transducer and the display head. Transducers, when activated by their associated transmitter circuits, send out ultrasonic pressure waves in an expanding pattern that can be simply expressed as a cone-shaped beam. Traditionally, sonar designers have been faced with a choice between wide viewing angle and high resolution.
A wide cone angle beam will cover a large viewing area and consequently aid in finding fish. However, there are certain disadvantages inherent in the use of wide cone angles. In particular, holes or drop-offs may be missed when the beam is wider than the hole or drop-off. Fish in a hole or along a drop-off will not be detected where the beam is wider than the hole or drop-off. Similarly, fish that are around submerged structure will be hidden unless they are above the peak of the structure. Also, wide beam target detection does not provide target placement within the beam, so that the user does not know where the fish is in relation to the boat.
A narrow cone angle beam will provide good detail of fish and underwater structure. However, in order to provide this detail, the viewing angle may be reduced by one-half or more.
Another problem found with existing fish finders is in determining target size. Since the strength of a sonar return is a function not only of target size but also of where the target is in the beam, a fish on the outer edge of the beam will appear smaller than if it were in the center of the beam. Similarly, a fish some distance from the transducer will appear smaller than if it were closer.
Another deficiency of previous fish finding systems is that the information transfer bandwidth between system and user is limited by primitive display formats. The two-dimensional displays of previous systems only provide a narrow slice of bottom structure information directly below the transducer. Therefore, slopes, channels or drop offs located to either side of the boat are not detected by the previous systems which use a single, narrow-width beam.
In prior art depth sounders, various methods are used to display the reflected sound pulses or "sonar returns" as a function of depth. Rotating disk lamps or "flashers", chart recorders, and numerical digital depth readouts are commonly employed to indicate the depth of a sonar return. These types of displays suffer from various disadvantages which are either inconvenient or annoying to a user.
One problem with many prior art apparatus is that a user must interpret the display to determine the bottom of the body of water since the display is typically a linear or curvilinear scale which extends to the extent of the capability of the apparatus. The bottom return in some devices such as chart recorders typically appears as a wide area or band on the display, but conditions such as thermocline and multiple returns caused by reflection from the boat bottom or other sources create additional sonar returns indicated as occurring at depths above or below the actual bottom, tending to make interpretation more difficult.
Some prior art linear or curvilinear displays such as flashers are only one-dimensional, in that the linear or curvilinear display can only display information for a single transmission. A sonar return subsequent to a currently-displayed return is erased or overwritten by new information. If a moving target is detected, the target such as a fish may disappear from the display after the next transmission, and the user may miss the target if the display has not been constantly watched.
In order to overcome the disadvantages of a one-dimensional display, other prior art sonar apparatus employ a chart-printing device or a cathode ray tube (CRT) to provide a two-dimensional display which lowers the risk of missing targets. Some of these devices include scale-changing features which allow different depth scales to be selected and associated with the display. However, when a scale change is made, a discontinuity at the point of the scale change makes interpretation of the display difficult. For example, if a target is detected at 15 feet on a 60-foot nominal scale, and the scale of the display is changed to 120 foot nominal depth, the previously detected target at 15 feet will remain in the same relative position on the display, since the device cannot go back and "rewrite" what has previously been written. However, new returns for the same target at 15 feet will appear at a different location on the display in the 120 foot nominal depth scale. Thus, the target will appear to have shifted upwardly on the display. Discontinuities such as these create confusion in display interpretation.
Some prior art sonar apparatus include a scale expansion feature wherein the depth scale is expanded by a predetermined factor of two. Other prior art devices include a scale expansion feature wherein an upper depth limit and a lower depth limit are keyed into the device, so that target data detected within these depth limits can be expanded to fill the display. Still other types of displays include prepicked scale expansion regions having a fixed number of fixed limit expansion regions.
All of these prior art approaches to display expansion are subject to criticism. The predetermined factor of two approach, while simple, cannot be used to "zero in" on a selected area for expansion. The selectable upper and lower limit approach requires the user to enter the limit data via a keypad, requiring mental calculations to determine the appropriate areas for display expansion. The prepicked expansion region approach suffers when a target of interest lies close to a boundary between expansion regions, so that selection of one expansion region followed by movement of the target requires the user to re-enter the expansion selection mode and select another expansion region.
Other problems exist in prior art sonar apparatus. A particular problem occurs in sonar apparatus having automatic gain control For example, previous systems have disclosed an apparatus wherein a microprocessor controls the gain of the receiver stage so that the gain of the receiver is automatically increased as the anticipated bottom depth increases. In this apparatus, the gain is set at a minimum at the time of and immediately succeeding a sonar transmission and as time increases, the receiver gain is increased in anticipation of weaker signals which correspond to greater depths.
A particular problem with variable gain amplifier circuits in that changing amplifier gain often creates transients which if not properly handled can appear as target returns. Typically, additional filters or other signal processing circuits are required to suppress the transients or otherwise assure that the transients are not treated as a valid return signal.
Moreover, troubleshooting of variable gain amplifiers is difficult in that a repair technician is required to have detailed information as to expected outputs for a wide range of input signals. This typically entails employing a variety of input signal settings and adjustments in order to isolate a particular faulty component in a variable gain amplifier.
Another problem frequently encountered in marine sonar apparatus is providing a watertight enclosure to protect the electrical circuitry which still allows a convenient user interface. Individual waterproof switches are expensive and are still prone to leaks in that a separate seal for each of a plurality of switches increases the probability that one or more of the switch seals will fail under adverse climatic conditions. Significant improvement in weatherability could be obtained by minimizing the number of places requiring weatherproof seals.
Therefore a need exists for a sonar fish detection apparatus capable of overcoming the above-discussed shortcomings of traditional systems.
Accordingly, it is an object of the present invention to provide novel sonar data collection, user interfaces and display formats that permit the user to more accurately comprehend the underwater environment.
It is an object of the present invention to provide a wide viewing angle simultaneously with detailed target resolution and fast bottom area coverage by providing multiple simultaneous sonar beams with a relatively small transducer.
It is a further object of the present invention to provide target size normalization in both depth and lateral planes.
It is a further object of the present invention to display multiple targets and bottom contours for the user on a real-time basis.
It is a further object of the present invention to distinguish targets from thermoclines and submerged structures on a real-time basis.
It is a further object of the present invention to provide a built-in means for interactively training an operator to use the sophisticated features of the invention.
It is a further object of the present invention to achieve minimum beam-to-beam acoustic interference through use of an optimally selected shape and material for the ceramic elements along with transducer and receiver multiplexing.
It is a further object of the present invention to achieve minimum beam-to-beam electrical interference through the use of shielded cable design, circuit design and board layout.
It is a further object of the present invention to achieve precise beam aiming so that the desired level of overlap occurs. Beam overlap eliminates dead spots in the coverage and allows accurate determination of target placement by means of the ratio of sonar target strength present in two adjacent and overlapping beams.